EP2233890A2 - Capteur capacitif et procédé de détection capacitive de l'écartement d'un objet - Google Patents

Capteur capacitif et procédé de détection capacitive de l'écartement d'un objet Download PDF

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Publication number
EP2233890A2
EP2233890A2 EP10405024A EP10405024A EP2233890A2 EP 2233890 A2 EP2233890 A2 EP 2233890A2 EP 10405024 A EP10405024 A EP 10405024A EP 10405024 A EP10405024 A EP 10405024A EP 2233890 A2 EP2233890 A2 EP 2233890A2
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EP
European Patent Office
Prior art keywords
operational amplifier
capacitor
measuring
capacitance
inverting
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP10405024A
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German (de)
English (en)
Other versions
EP2233890A3 (fr
Inventor
Werner Hinn
Daniel BRÄNDLE
Lars Kamm
Ueli Hafner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Baumer Innotec AG
Original Assignee
Baumer Innotec AG
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Filing date
Publication date
Application filed by Baumer Innotec AG filed Critical Baumer Innotec AG
Publication of EP2233890A2 publication Critical patent/EP2233890A2/fr
Publication of EP2233890A3 publication Critical patent/EP2233890A3/fr
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance

Definitions

  • the invention relates to a capacitive sensor and a method for capacitive detection of an object distance according to the features of patent claims 1 and 8.
  • Capacitive proximity switches are widely used in process and automation technology for detecting electrically conductive or non-conductive objects, for example for detecting moving machine parts or filling levels in containers.
  • this measuring capacity is part of an oscillator, eg an RC oscillator.
  • the oscillation condition of this oscillator is only fulfilled if the value of the measuring capacity exceeds a minimum value due to external influences (approximation of the measuring object).
  • the switching state of the sensor output depends on the oscillation amplitude of the oscillator. As soon as this oscillation amplitude exceeds a predetermined or predefinable value, the switching state of the sensor output changes.
  • a switching distance can eg by means of a Potentiometer as adjusting the resonant frequency of the oscillator or alternatively the reference voltage for the comparison of the oscillation amplitude can be changed.
  • the oscillation amplitude could also be detected and processed further by means of analog or digital signal processing.
  • this requires relatively complex electronic circuits with a correspondingly high space requirement.
  • reaction time for oscillatory solutions is relatively long. This is especially true if in addition analog-to-digital converters are used to digitize analog measurement signals for further processing.
  • a capacitance measuring circuit in which a measuring capacity is detected with the inclusion of a sigma-delta converter.
  • the measuring capacitance is clocked via a switch with a reference voltage source and then connected to a passive network, in each case a charge transfer to the passive network takes place. As soon as the charge exceeds a threshold, it is reduced by a predetermined amount and the process is repeated.
  • a digital signal in the form of a bit stream is generated as a function of the measuring capacity and the passive network. This bitstream is converted by a filter to a desired output.
  • parasitic capacitances and common-mode voltages can lead to errors in the measurement result.
  • different operating voltages can cause measurement errors.
  • An object of the present invention is to provide a capacitive sensor and a method for easily and accurately detecting a measuring capacity.
  • the inventive capacitive sensor comprises an integrated electronic circuit with a delta-sigma converter in fully differential design.
  • the electronic circuit is preferably formed on a single chip as an application-specific integrated electronic circuit, called ASIC for short.
  • the outputs of the operational amplifier are connected to a system clock-triggered triggering device for generating a bitstream, this bitstream having a mean value reciprocal to the measuring capacitance.
  • a measuring capacitor whose measuring capacity is variable by external influences, and a reference capacitor with a fixed reference capacitance are connected to input interfaces or inputs of the integrated circuit.
  • the measuring capacitor and / or the reference capacitor could also be integrated into the electronic circuit.
  • Both the measuring capacitor and the reference capacitor each one of the electrodes is connected to the ground potential or to a fixed reference potential.
  • the respective other electrodes can be connected via a switching device to the non-inverting and the inverting input of the operational amplifier.
  • the switching device is controlled by an electronic control unit and includes Switching elements or switches, which are closed and opened depending on the initial state of the triggering device.
  • the control electronics are preferably partially or fully integrated in the electronic circuit, which also includes the delta-sigma converter.
  • the electronic circuit comprises further input interfaces for compensation capacitances, which correspond to the parasitic capacitances of the reference capacitor and of the measuring capacitor. These input interfaces are also connectable via the switching device with the inverting and the non-inverting input of the operational amplifier.
  • the four inputs are connected in a four-phase operation in an order prescribed for each of these inputs respectively with the inverting and the non-inverting input of the operational amplifier and with two different fixed potentials (ground potential and operating voltage potential).
  • the phase change is triggered by the system clock.
  • the inverting input and the non-inverting input of the operational amplifier are alternately connected during each two of the four phases with the common-mode potential of the operational amplifier.
  • the voltage difference between the two outputs of the operational amplifier are respectively incremented or decremented by specific voltage values with each pass of a four-phase cycle, depending on the output state of the trigger device .
  • These voltage values are only dependent on the measuring capacitance, the reference capacitance, the integration capacitances and the operating voltage, but not on the common-mode voltage and parasitic capacitances. Faults or errors of the measurement result due to circuit-related parasitic capacitances and due to the common-mode voltage of the operational amplifier are thus eliminated in the inventive capacitive sensor.
  • the two integration capacities are specified with identical value. In this case, the average voltage at the output of the electronic circuit adjusts itself to a mean voltage value which is inversely proportional to the measuring capacity.
  • FIG. 1 shows a simplified first circuit arrangement for detecting the measuring capacitance C S of a measuring capacitor 1.
  • the measuring capacitor 1 and a reference capacitor 3 with a reference capacitance C R are connected via a switching device to the inverting and the non-inverting input of a fully differential operational amplifier 7.
  • the switching device comprises a plurality of switching elements or electronic switches 5, which are framed by a thin dotted line 5a.
  • a first integration capacitor 9 is arranged with a first integration capacitance C I01 .
  • a second integration capacitor 11 having a second integration capacitance C I23 is arranged in a feedback branch between the positive output and the inverting input of the operational amplifier 7.
  • the inverting and the non-inverting input of the operational amplifier 7 are connected to the common-mode potential.
  • the outputs of the operational amplifier 7 are connected to the inputs of a triggered by a system clock (clock) trigger device 15.
  • the switch 13 and the switch 5 are controlled by a (not shown) control electronics.
  • the control electronics can be arranged partially or completely together with the circuit arrangement on a common chip. Alternatively, the control electronics can also be designed as a separate part and connected to the integrated circuit on a chip.
  • the control electronics can also be designed to perform other tasks, eg for providing a stabilized voltage V DD , for generating the system clock and / or for further processing of the signals at the output of the trigger device 15 (point " D ").
  • Two switches 5 framed by a bold broken line 5b are controllable by the control electronics as a function of the initial state of the triggering device 15.
  • These switches 5 are designed to interrupt the connection between the measuring capacitor 1 and the inverting or the non-inverting input of the operational amplifier 7 and to close again. They are closed when the signal level V DD (also referred to as "V H " or “H”) is at point D; they are open when the signal level at point D is "V L " or "L".
  • V DD also referred to as "V H " or "H”
  • V L the signal level at point D is "V L " or "L”.
  • the connections to the Reference capacitor 3 is interrupted in an analogous manner and closed again.
  • the other two switches 5 in FIG. 1 are switched by the control electronics in the system clock.
  • the inputs of the circuit arrangement, to which the measuring capacitor 1 and the reference capacitor 3 are connected connected in a four-phase cycle with the inverting and the non-inverting input of the operational amplifier 7 and with V L and V H.
  • the sequence of the individual connections corresponds to that of FIG. 2 illustrated extended embodiment.
  • the circuit arrangement comprises a first compensation input, which is designed analogously to the sensor input and likewise has an at least approximately equal parasitic capacitance C PS .
  • no measuring capacitor 1 is connected to the first compensation input.
  • the first compensation input is analogous to the measuring input via switch 5 of the switching device 5a connectable to the inputs of the operational amplifier 7 and to V L and V H , the connections to the operational amplifier 7 being interruptible by the control electronics as a function of the initial state of the trigger device 15.
  • the circuit arrangement comprises a second compensation input, which is designed analogously to the reference input and likewise has an at least approximately equal parasitic capacitance C PR .
  • no reference capacitor 3 is connected to the second compensation input.
  • FIG. 3 shows a diagram in which the timing of the system clock (Clock) and the dependent phase clocks ⁇ 0 , ⁇ 1 , ⁇ 2 , ⁇ 3 , ⁇ 2 + ⁇ 3 and ⁇ 0 + ⁇ 1 are shown.
  • I + non-inverting input of the operational amplifier 7
  • I- inverting input of the operational amplifier 7
  • V L reference potential (ground)
  • D can have the values 0 or 1, depending on whether the output of the triggering device is 15 V L or V H and, correspondingly, the switches 5 framed by the line 5b are opened or closed.
  • FIGS. 4 to 7 Simplify the configurations during the individual clock phases for a simplified circuit without parasitic capacitances, as in FIG. 1 is shown. For better clarity, the triggering device 15 is not shown in each case.
  • V C S ( ⁇ ) at the measurement capacitor 1, V C R ( ⁇ ) are set forth for the individual phases at the reference capacitor 3, V C I 01 ( ⁇ ) at the first integration capacity 9, V c I 23 ( ⁇ ) at the second integration capacitance and V out ( ⁇ ) between the outputs of the operational amplifier 7.
  • the time scale (2 ⁇ s / unit) is the same for all curves K1 to K4.
  • the voltage scales at curves K2, K3 and K4 are given in V / unit or mV / unit.
  • the values of the measuring capacity CS are 1.12pF at FIG. 8 ; 560fF at FIG. 9 ; 280fF at FIG. 10 and 140fF at FIG. 11 ,
  • the output signal (D) of the triggering device 15 consists of square-wave signals, each during four System clocks (clock) or during a 4-phase cycle have the potential V H and follow one another at a time interval which is inversely proportional to the measuring capacitance C S.
  • this signal can be output as a pulse-width-modulated distance signal.
  • the signal can also be further processed digitally, wherein the time intervals of successive pulses are evaluated.
  • the transfer function or the characteristic of the sensor can be specified individually.
  • the capacitive sensor can be generated from the output signal of the trigger device 15, for example by a downstream filter in a simple manner, an at least approximately - linearized function of the sensor to be detected object distance or the reciprocal of the measuring capacitance C s represents.
  • the values of the integration capacitances C I01 and C I23 and the reference capacitance C R can be determined depending on the desired measuring range and / or the required resolution or accuracy of the sensor.
  • each of the integration capacitances C I01 and C I23 can be varied, for example, by the control electronics, in that two or more capacitors are connected in parallel by electronic switches and together Integrating capacity C I01 or C I23 form.
  • the value of the externally connected to the chip reference capacitance C R can be changed and adapted to the respective requirements.
  • capacitive analog distance sensors it is also possible to design proximity switches or any other sensors in which a capacitance must be detected in the manner according to the invention.
  • the output of the sensor behaves at least approximately proportional to the distance of the target, and the sensitivity and accuracy of the sensor are maintained up to greater distances.
  • the measuring range is not limited primarily by the sensitivity decreasing with increasing distance (change of the output variable per millimeter change in distance), but by the signal-to-noise ratio, which deteriorates with increasing distance. Since no ideal plate capacitors are used in practice, field distortions at the edge of the electrodes can cause slight deviations of the output characteristic, which indicates the dependence of the measured quantity 1 / C on the target distance.
  • the pulse density of the output signal i.e., the number of pulses per unit of time
  • increases with increasing distance which at larger distances can result in a larger measurement bandwidth and thus a shorter sensor response time.
EP10405024.0A 2009-02-11 2010-02-10 Capteur capacitif et procédé de détection capacitive de l'écartement d'un objet Withdrawn EP2233890A3 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH00203/09A CH700376A2 (de) 2009-02-11 2009-02-11 Kapazitiver Sensor und Verfahren zur kapazitiven Erfassung eines Objektabstandes.

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EP2233890A2 true EP2233890A2 (fr) 2010-09-29
EP2233890A3 EP2233890A3 (fr) 2014-12-24

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3415872A1 (fr) * 2017-05-19 2018-12-19 Simmonds Precision Products, Inc. Conditionneur de signal à précision élevée et faible puissance
CN114915290A (zh) * 2022-04-25 2022-08-16 西安航天民芯科技有限公司 一种单极板电容直接转换传感器寄生电容平衡电路及方法

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102013201704A1 (de) * 2013-02-01 2014-08-07 Di-Soric Gmbh & Co. Kg Kapazitive Sensoranordnung und kapazitives Messverfahren mit Kompensation parasitärer Kapazitäten
EP3663779B1 (fr) * 2018-12-05 2021-10-06 Nxp B.V. Appareil et procédé pour mesurer une capacité et capteur d'empreintes digitales l'utilisant
CN112484810A (zh) * 2020-12-02 2021-03-12 上海钛米机器人股份有限公司 一种溶液检测装置及方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006125639A1 (fr) 2005-05-25 2006-11-30 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Circuit de mesure de capacite
WO2006132960A1 (fr) 2005-06-03 2006-12-14 Synaptics Incorporated Methodes et systemes de detection d'une capacitance utilisant des techniques de mesure sigma-delta

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Publication number Priority date Publication date Assignee Title
ITTO20010699A1 (it) * 2001-07-17 2003-01-17 St Microelectronics Srl Metodo e circuito di rilevamento di spostamenti tramite sensori micro-elettro-meccanici con compensazione di capacita' parassite e di movime
EP1861723B1 (fr) * 2005-03-09 2017-04-19 Analog Devices, Inc. Circuit d'interface de condensateur a une borne
DE102005028507B3 (de) * 2005-06-17 2006-11-30 Texas Instruments Deutschland Gmbh Verfahren zur Kapazitäts-Spannungs-Wandlung und Kapazitäts-Spannungs-Wandler
EP1790988B1 (fr) * 2005-11-29 2017-01-18 STMicroelectronics Srl Circuit de détection dans une interface de détection utilisant un capteur capacitif différentiel avec contrôle du mode commun à l'entrée
EP1811309B1 (fr) * 2006-01-20 2009-10-07 STMicroelectronics S.r.l. Dispositif détecteur de chute libre et méthode de détection de chute libre

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006125639A1 (fr) 2005-05-25 2006-11-30 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Circuit de mesure de capacite
WO2006132960A1 (fr) 2005-06-03 2006-12-14 Synaptics Incorporated Methodes et systemes de detection d'une capacitance utilisant des techniques de mesure sigma-delta

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3415872A1 (fr) * 2017-05-19 2018-12-19 Simmonds Precision Products, Inc. Conditionneur de signal à précision élevée et faible puissance
US10641620B2 (en) 2017-05-19 2020-05-05 Simmonds Precision Products, Inc. High accuracy, low power signal conditioner
CN114915290A (zh) * 2022-04-25 2022-08-16 西安航天民芯科技有限公司 一种单极板电容直接转换传感器寄生电容平衡电路及方法

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EP2233890A3 (fr) 2014-12-24
CH700376A2 (de) 2010-08-13

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